Protective system and apparatus for discharge tubes



y 1939- R. A. HENDERSON ET AL 2,

PROTECTIVE SYSTEM AND APPARATUS FOR DISCHARGE TUBES Filed Nov. 25, 1936 Inventor Gttorneg PATENT OFFICE PROTECTIVE SYSTEM AND APPARATUS FOR DISCHARGE TUBES Roy A. Henderson, West Collingswood, and Vernon D. llauck, Merchantville, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application November 25, 1936, Serial No. 112,700

Claims.

This invention relates to protective systems and devices for fluid cooled thermionic discharge tubes.

The prior art is replete with apparatus designed 5 to prevent discharge tubes from overheating. Thus, it has previously been proposed to provide a thermally actuated electric switch connected in series between the tube and its source of current whereby the source may be disconnected from the tube at a critical temperature. Since it is usually only high-powered tubes that merit protective systems it follows that the thermal responsive switches employed in prior art systems must be of rugged construction in order to carry the current and to break the circuit between the tube and its source. Instances have arisen wherein discharge tubes have been damaged due to failure to supply a switch of rugged enough construction, or because of failure of the thermal switch contacts to break cleanly.

Protective systems are also known wherein the thermal responsive element per se forms no part of the current transfer circuit but serves rather as a mechanical hand for supplying the torque or other positive force required to disengage complementary circuit breaking elements. Protective systems of the prior art employing devices of this type are at least as cumbersome as the devices they are designed to supplant and are further objectionable because of a tendency to stick, especially after long periods of idleness.

Accordingly, an object of the present invention is to provide a simple, inexpensive troublefree thermally actuated protective system for discharge tubes.

Another object of the invention is to provide a system of the type described employing a trigger-like thermal responsive element which, per se, forms no part of the current transfer circuit.

Another object of the invention is to provide a protective system for fluid cooled discharge tubes operable to' deenergize the tube in the event of a change in the 'rate of flow of the cooling fluid and including supplementary means operable to disconnect said tube in the event of failure of the cooling means to accomplish its purpose.

Certain details of construction together with other objects and advantages will be apparent and the invention itself will be best understood by reference to the following detailed description when read in connection with the accompanying drawing, wherein Fig. 1 shows schematically a thermionic discharge tube and cooling mechanism therefor, including a protective system constructed in accordance with the principle of the invention,

Fig. 2 is a longitudinal sectional view, and

Fig. 3 is an elevational view of a preferred form of a thermally actuated release.

In the drawing, l0 designates a vacuum tube having a filament indicated by leads II, a grid and lead i4 therefor, and an external dependent anode IS. The anode portion of the tube is seated within a metal structure which is constituted essentially of a plurality of heat radiating fins l8 which extend outwardly from an annular or cylindrical frame 20 contiguous the anode. The fins I 8 flare outwardly adjacent the main body portion of the tube and form a shoulder 22 for supporting the structure upon a metal annulus 24 which surrounds the peripheral rim of a hollow insulating conduit section 26. A panel or shelf 28, suitably orificed to permit the passage of air to the conduit, supports the assembly in which the tube is seated. A tray 30, similarly orificed and having a handle 32, may be provided intermediate the shelf 28 and insulating section 26, to permit the apparatus thereabove to be moved for purposes of inspection and repair.

The hollow insulating section 25 communicates with a second conduit section 34 beneath the shelf 26. Section 34 is connected as by a more or less flexible coupling 36 to the mouth of a blower 38 which provides a forced draft of air for dissipating the heat transferred from the tube ill to the cooling fins IS. The blower 38 rests upon a vibration-damping base 40 and is energized by a motor, indicated symbolically at 42. Motor 42 is actuated by a switch 44 connecting it to a suitable source of current, not shown.

The interior of the conduit section 34 is provided with a valve which may conveniently be constituted by plate or disc 46, pivoted at 48, to p permit the passage of air when it is forced open by the draft from the blower. An external arm 50, also pivoted at 48, carries a mercury switch 52 which operates in a manner later described to cut off the current to the discharge tube In in response to any undesired change in the rate of flow of air in the conduit before such change can be reflected by an increase in the temperature about the anode of the tube.

An overtemperature release, indicated generally at 60, is supported on the fin structure adjacent the anode of the tube, whereby, in the event of failure of the valve 46 or switch 52 to operate, or in the event of excessive temperature arising from this or any other cause, the tube will be de-energized.

The overtemperature release 60 may be constituted, in accordance with the invention, by the device shown greatly enlarged in Figs. 2 and 3. As more clearly shown in these figures, the device comprises a hollow metal cylinder 62 having a section 64 of its outer surface flattened and having a continuing section of its surface 66 cut away to expose a portion of the interior of the cylinder. The bore of the cylinder 62 accommodates a somewhat loosely fitting metal rod 68 which extends beyond the end oi the cylinder and terminates in an eyelet 18 for receiving an ejecting cord 80 (Fig. 1). Abl-metallic strip 12 is afilxed, as by screw 14, to the flat portion 64 of the outer surface of the cylinder. The free end ofstrip 12 extends to the cut away portion of the cylinder, at which point it curves inwardly and terminates within a circumferential notch 68" in rod 88, whereby the rod is normally maintained against withdrawal i'rom the bore of the cylinder. The bi-metallic strip I2 is preferably constructed to flex at a. critical temperature (say, 160 0.). When this temperature is reached, the terminal end 01' the strip becomes unscated, permitting the rod to be withdrawn.

Referring again to Fig. 1. The releasable rod of the thermo-regulator 60 is connected by a taut insulating cord 80 to aswitch 82 which is normally maintained closed against the tension of a spring 84 by the cord. When the thermal actuated trigger 12 (Figs. 2 and 3) holding the rod 68 is released, the force holding switch 82 closed against the tension of its biasing spring 84 no longer exists so that the switch will open.

Switch 82 and mercury switch 62 are connected in series in a branch line 86 to a main line 88 which is connected to a source of current, not shown, which supplies current for energizing the tube. A magnetically controlled switch 90, biased to open as by means of gravity or by a spring 92 is included in the circuit connecting leads 86 to the primary source. When switch 90 is closed the circuit is completed to a suitable current translating device Hill, the output of which is transferred through an impedance I82, line I04, through metal ring 24 to the anode l6 of the tube. Switch 90 can be maintained closed only when its holding magnet indicated symbolicaliy at 94 is energized by current flowing through solenoid 96. To complete the circuit through solenoid 96 both switch 62 and switch 82 must be closed. To complete the circuit through the mercury switch 52, blower 88 must create a continuous draft suiiicient to maintain valve 46, and hence arm 58, at a required angle.

It is thus apparent that the blower 38 must beoperating before switch 90, controlling the current supply to tube Hi, can be closed.

Should the blower fail during operation, valve 46 will close, switch 52 open, and since the solenoid 96 is thereby instantly deenergized, switch 90 will likewise open, cutting oil the current sup ply for the tube.

If the tube overheats either because the air supplied to it by the blower is too hot, or by reason of failure of the valve 46 or mercury switch 52 to operate, then the terminal end of the b1- metallic strip 12 of the thermo-regulator 60 will cease to engage the rod 68. The force, exerted through cord 80, normally holding switch 82 .closed is thereby removed and this switch will fly open, breaking the flow of current through the solenoid 96 and causing a break in the circuit between the source and the tube. Since a potential diflerence of several thousands of volts may exist between anode l6 and switch 82, the mechanical link (exemplified by cord 80) therebetween must include, or be constituted of in- 0 sulating material.

In the illustrated embodiment oi the invention the filament oi the tube is shown connected through a fllament transformer I It, leads I I2 and switch 90 to the main line 88 whereby upon opening of the switch 80 the cathode I2 is deenergized. Grid lead l4 will be understood to be connected to an appropriate circuit, not shown.

While the invention has been described in connection with an air-cooled tube, it is to be understood that the invention is not limited to such application as the disclosure in this respect is merely illustrative Ior purposes oi explaining the inventive concept.

What is claimed is:

1. In combination, a discharge tube, a source of current, a switch for controlling the application of current from said source to said tube, said switch being mounted remote from said tube, biasing means tending to open saidswitch, tensioned insulating means for holding said switch closed against the force of said biasing means. and a thermal responsive element supported adiacent said tube for releasing the tension on said insulating means.

2. In combination, a discharge tube having a plurality of electrodes, a source of voltage, connections from said source to said tube, means for causing a cooling fluid stream to flow adjacent one of said electrodes, means directly responsive to a change in the rate of flow of said fluid stream for disconnecting said source from said tube, and supplementary means for disconnecting said source from said tube, said supplementary means comprising a switch remote from said tube, biasing means tending to open said switch, tensioned insulating means for holding said switch closed against the force of said biasing means, and a thermal responsive element supported adjacent said tube for releasing the tension on said insulating means.

3. In combination, a discharge tube having a plurality oi electrodes, means for causing a cooling fluid stream to flow adjacent one of said electrodes, a source of voltage, a circuit from said source to said tube, a movable armature and contact therefor disposed in said circuit, a solenoid arranged to close said movable armature into engagement with said contact when said solenoid is energized, a control circuit connected with said solenoid, a pair of series connected switches in said control circuit, means responsive to a change in therate of flow of said fluid stream for opening one of said switches and means responsive to a thermal condition of said tube for opening the other of said switches.

4. In apparatus of the type described, an overtemperature release comprising a hollow cylinder, a rod in the bore oi! said cylinder, a notch in said rod, said cylinder having a portion of its wall cut away to expose said notch, a thermal responsive strip fixed at one end thereof to the outer wall of said cylinder and having its free end normally seated in the notch in said rod.

5. The invention set forth in claim 4 wherein means are provided for applying a positive force to said rod for ejecting it from said cylinder upon disengagement of said thermal responsive element with said notch.

ROY A. HENDERSON. VERNON D. HAUCK. 

